Scale Calculator

Converts between real length and length on a drawing, map or model at a scale such as 1:100, and finds the scale from two lengths. It also converts areas and volumes, gives the copy percentage for changing scale and lists model scales.

How to use

1. On "Convert", type the "Scale" as 1:100, 1/50 or 2:1, or press one of the "Common scales".
2. Type in "Real length" or "Length on the drawing, map or model"; the other box is calculated. Each box has its own unit.
3. If you know two lengths but not the scale, use "Find the scale". The nearest standard scales are shown as well.
4. Use "Area and volume" for areas, "Change scale" for print percentages and "Model scales" for models.

How it works

• At a scale of 1:n, drawing length = real length ÷ n and real length = drawing length × n. Areas change by n² and volumes by n³.
• An architect's scale x" = 1'-0" is 1:(12 ÷ x), and an engineer's scale 1" = x' is 1:(12 × x). For example, 1/8" = 1'-0" is 1:96.
• When printing, turn off "fit to page", then check a known length with a ruler.

Questions and answers

How does a 1:100 scale work?

1 unit on the drawing is 100 units in reality. A real length of 5 m is 5 cm on the drawing, and 1 cm on the drawing is 1 m in reality.

On a 1:50,000 map, how far is 4 cm?

4 cm × 50,000 = 200,000 cm = 2 km.

What percentage turns a 1:50 drawing into 1:100?

50 ÷ 100 × 100 = 50%, a reduction. To go from 1:100 to 1:50, enlarge to 200%.

What real area is 1 cm² on a 1:100 plan?

Areas grow by 100 × 100 = 10,000 times, so it is 1 m².